Systematic analysis of Treponema pallidum gene expression under host infection related conditions

University Of Texas Hlth Sci Ctr Houston, Houston TX

Investigators

Abstract

PROJECT SUMMARY/ABSTRACT Cases of venereal and congenital syphilis are spiking in the United States, reaching levels not seen since the 1950s according to the CDC. Despite the discovery more than 100 years ago that Treponema pallidum subsp. pallidum (Tp) causes syphilis, the biology and pathogenesis of Tp are poorly understood. A major road block to Tp research and vaccine development has been the inability to continuously culture this bacterium in vitro and the lack of methods to sensitively detect Tp in host tissues. These obstacles have recently been removed with the establishment of a continuous in vitro culture system for Tp by the Edmondson/Norris group and the development of droplet digital PCR (ddPCR). The overall goal of this project is to determine how different genetic factors, changes in host-relevant environmental conditions, and host interactions impact Tp gene expression. The central hypothesis is that Tp alters its gene expression in response to changes in oxygen concentration, temperature, and host interactions, which allows this pathogen to successfully colonize and disseminate within and between hosts. In Aim 1, the impact of different temperatures, oxygen concentrations, and host cell interactions on Tp gene expression will be investigated by RNA-seq and reverse transcription ddPCR using the Nichols and SS14 strains, which represent the two clades of Tp. In Aim 2, the abundance of Tp in a diverse set of host tissues will be determined during infections of rabbits. How Tp gene expression changes during colonization of different rabbit tissues will also be examined. The significance of the proposed research is that it will establish for the first time how changes in host-relevant environmental conditions impact Tp gene expression, and indicate which fitness and virulence factors are necessary for Tp infection of specific tissues and which ones are needed for all infection stages. Finally, these studies will reveal how the presence or absence of host cells impacts Tp gene expression during in vitro growth. This proposed research will utilize a new, innovative method for culturing Tp in vitro in the absence of host cells (axenic culture) and the innovative technique of ddPCR for detecting even extremely low levels of Tp in different host tissues. Finally, the proposed studies are also innovative in design since for the first time the differences in Tp gene expression in different host tissues, under different host-relevant temperatures and O2 concentrations, and in the presence or absence of host cells during growth in vitro will be examined.